Preparation of hierarchical nano-SAPO-11 zeolites as catalysts for the synthesis of 2,6-dimethylnaphthalene
As a microporous zeolite,SAPO-11 zeolites usually have a large particle size,and SAPO-11 with a small particle size has shorter pores,which facilitate better diffusion of molecules and thus enhance catalytic activity.However,this also leads to poorer stability.How to further synthesize hierarchical nano-SAPO-11 zeolites on the basis of hydrothermal method is a great challenge.Based on the hy-drothermal method,SAPO-11 zeolites were prepared by aging treatment with the precursor gel.Among them,the SAPO-11 zeolites pre-pared by stirring aging treatment at 80 ℃ has the smallest crystal size.It can be seen by SEM that the S1 1-80 ℃-stirring zeolite show a uniform nanorod-like structure,these nanorods have a diameter of about 500-700 nm and a length of about 2-4 μm.The N2 adsorption-desorption isotherms and pore size distribution curve reveal that the SAPO-11 zeolite treated by aging has a larger specific surface are-a compared to conventional SAPO-11.Specifically,zeolites prepared by agitation aging show a higher specific surface area and pore vol-ume for micropores,but lower values for mesopores compared to those prepared by static aging.The NH3-TPD curves characterization of the acidic properties shows that all SAPO-11 zeolites synthesized with aging treatment have reduced acidity.2-Methylnaphthalene(2-MN),which is mainly derived from coal tar,can be used to prepare 2,6-dimethylnaphthalene(2,6-DMN),and then be used to synthesize high-end polyester.Therefore,the above-mentioned hierarchical nano-SAPO-11 zeolites were applied to catalyze the alkyla-tion reaction of 2-methylnaphthalene.The results show that the SAPO-11 zeolites prepared by aging treatment have 77.8％initial conver-sion of 2-MN,20.4％initial selectivity,1.13 molar ratio of 2,6-DMN/2,7-DMN,and the highest selectivity of 2,6-DMN of 39.9％at the 4th hour of reaction.The shape selection catalytic mechanism of SAPO-11 molecular sieve was revealed by series characterization.
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